The term radar is an acronym that stands for “radio detection and ranging.” A radar system transmits radio frequency (RF) signals in a predetermined direction (i.e., a bearing or angle-of-arrival) with the intention of contacting or illuminating moving objects (“contacts”). When the transmitted radar signal illuminates a contact, a return signal is reflected back toward the radar receiver. The return signal is detected if the return signal is stronger than any noise signals that may be present in the receiver. A contact's bearing corresponds to the direction of the transmitted radar signal because the signal travels at the speed of light. The distance, or “range,” is determined by measuring the time between signal transmission and the reception of the return signal. Thus, radar systems are commonly used in commercial and military settings for purposes of identifying and tracking a radar contacts within a predetermined search volume.
Radar trackers are established components of radar systems. As radar systems receive reflected signals, or plots, from targets, radar trackers associate the most recent plot with prior plots from the same target. Associating several plots in this way creates a track representing the path a given target has followed. By creating these tracks for each target, radar systems are better able to reject false positives, to estimate the current speed and heading of a target, to remove measurement error from positions estimates, and to identify the paths and origins of multiple unique targets, among other benefits. Furthermore, radars tracker may also improve the accuracy of each received signal from a given target, by shifting it to fit a smooth curve with the target's established track. In this way, ambiguities or inaccuracies in each received signal can be accounted for and corrected.
Accuracy and range may be further improved with a radar tracker by associating multiple radar systems to a single tracker; this is known as a multi-radar or fusion tracking. Fusion tracking systems offer a number of advantages over single-sensor radar, because they can provide improved accuracy based on geometric diversity and an improved update rate, particularly if the sensors are transmitting asynchronously. Furthermore, multiradar systems can track targets when one sensor is blocked by terrain, or the target is out of range, if the other sensor maintains a clear view of the target.
In fusion tracking systems, it is necessary to the convert the coordinate system of the sensors to a central, often Cartesian, coordinate system. This is because each sensor naturally uses a spherical coordinate system that is centered around itself, providing measurements of range, azimuth angle, elevation angle, and range-rate. Thus to combine each sensor in a fusion system, the data from at least some sensors need to be transferred into another, common coordinate system, not referenced to those sensors.
While some of the data from each sensor may be easily transferred, range-rate may not be easily transformed into another coordinate system because it represents only a component of velocity, and is implicitly referenced to the sensor. Some methods have been developed to utilize range-rate in a fusion tracking system; however, these methods are inefficient and prohibitively computationally intensive.
Accordingly, there is a continued need in the art for a fusion tracking system that utilizes range-rate in an effective and computationally efficient manner.